This invention relates to a liquid crystal mixture containing an ionic substance which can be suitably used in the display mode utilizing the dynamic scattering effect in a positive type guest-host color liquid crystal display device.
The display system using the dynamic scattering mode (DSM) of a liquid crystal has been used in various display devices such as pocketable or desk-top calculators, timepieces, and so forth. The dynamic scattering mode of a liquid crystal refers to scattering of incident light that takes place as a result of local disturbance of the orientation of liquid crystal molecules due to the flow of ions inside a nematic liquid crystal with the application of an electric field to the nematic liquid crystal having negative dielectric anisotropy. Display can be effected by making use of this phenomenon.
There must be an electric charge in a liquid crystal to cause the dynamic scattering mode of the liquid crystal occurs. To this end, an ionic substance is generally added as a dopant to the nematic liquid crystal having negative dielectric anisotropy. However, with the application of an electric field, a conventional ionic substance is likely to cause a chemical reaction in a liquid crystal composition containing a dichroic dye added for the color liquid crystal display, an optically active substance and the like, and has low dissolution stability in the nematic liquid crystal having negative dielectric anisotropy. Hence, the resulting color liquid crystal display device has short service life and low reliability.